1. Field of the Invention
The present invention relates to devices for cutting and joining plant shoots, and more particularly to a device for mechanically grafting plant scion onto plant stock, especially of grapevine.
2. Description of the Prior Art
Grafting involves the end-to-end connection of a shoot of a superior plant, so-called scion, onto a branch or shoot of an inferior plant, so-called stock. Several different kinds of graft joints are known, among them cleft joints, splice joints, tongue joints, and saddle joints, all using acutely angled cuts on the extremities of the scion and stock. The more common types of graft joints are the tongue joint and the saddle joint which produce a wedging action between the joined extremities. Generally, the manually performed cutting operations are time consuming and required considerable skill and physical effort.
It has therefore already been suggested to mechanize the grafting process by using a device in which the graft cutting is performed by a guided knife blade. A known device of this type has a thin knife blade which is shaped so as to produce the graft cut for both the scion and the stock, the former having a central longitudinal protrusion, much like a tooth, which engages a matching recess in the latter. The shape of the tooth resembles the Greek letter omega, or a U-shape with undercut sides, with the result that the joined extremities of scion and stock are longitudinally interlocked. In order to produce this cut, the shaped knife blade is attached to a vertically movable carriage whose motion may be produced by the means of a treadle or by means of a pneumatic linear actuator. The scion or stock to be so cut is held in place inside a V-groove.
This known device further features a means for retaining the cut scion on the shaped knife, while the latter cuts the extremity of the stock in a second cutting stroke, so that, as the shaped scion and stock are removed from the omega-shaped knife of the device, they are at the same time also joined together. The means which removes the scion from the shaped knife thus operates only during every second knife stroke, requiring a special mechanism for its operation. This mechanism includes an ejector member which is vertically movable with the knife blade, except when its upward motion is stopped through a transversely movable latch pin, thereby causing the ejector member to remove the scion from the knife blade. The latch pin is spring-biased away from the ejector member and driven towards the latter by means of a disc cam whose large and small radii engage and release the latch pin, respectively. The rotation of the disc cam is such that it advances during each stroke of the knife blade and carriage from a large radius to a small radius, or vice versa, a ratchet wheel on the disc cam shaft being engaged by the carriage during each downward stroke, thereby producing the disc cam motion.
This device is complex and subject to wear and noise on the latch driving mechanism. The complexity of the latter also means that the device is comparatively expensive to manufacture.